Printing apparatus of the general type with which the present invention is concerned are known. They operate with a supply of tape arranged to receive an image and a means for transferring the image onto the tape. In one known device, there is a tape holding case which holds a supply of image receiving tape and a supply of an image transfer ribbon, the image receiving tape and the transfer ribbon being passed in overlap through a printing zone of the printing device. At the print zone, a thermal print head cooperates with a platen to transfer an image from the transfer ribbon to the tape. A printing device operating with a tape holding case of this type is described for example in EP-A-0267890 (Varitronics, Inc.). Other printing devices have been made in which letters are transferred to an image receiving tape by a dry lettering or dry film impression process. In all of these printing devices, the construction of the image receiving tape is substantially the same. That is, it comprises an upper layer for receiving an image which is secured to a releasable backing layer by a layer of adhesive.
The upper layer can either receive an image on its top surface, its lower surface being secured to the releasable backing layer by a layer of adhesive or alternatively the upper layer can be transparent and can receive an image on one of its faces printed as a mirror image so that it is viewed the correct way round through the other surface of the tape. In this case, a double sided adhesive layer can be secured to the upper layer, this double sided adhesive layer having a releasable backing layer. This latter arrangement is described for example in EP-A-0322918 (Brother Kogyo Kabushiki Kaisha).
With such printing devices, it is important to be able to determine when the tape holding case used with the device has exhausted its supply of image receiving tape so that a new tape holding case can be inserted into the device. If the printing device is run with no image receiving tape there is a danger that the print head or platen will be damaged by overheating. Damage to the platen can also result if an image is transferred to it by the print head operating with no image receiving tape.
Furthermore, it is desirable for printing apparatus of this type to be able to operate with image receiving tapes of different widths. For this, the apparatus should include a way of identifying the width of tape within the tape holding case automatically so that the user does not have to concern himself with setting the apparatus for different tape widths. There is a danger if the user is called upon to set the tape width that the tape width will be incorrectly set.